Recently, there has been an increasing demand for home TV sets representing AV equipments and display devices for use in OA equipments of improved characteristics such as light weight, thin structure, low power consumption, high definition performance and large screen, etc. To meet these demand, the development of display devices such as a CRT (cathode ray tube) display, an LCD (liquid crystal display), a PDP (plasma display panel), an EL (electro luminescent) display, and an LED (light emitting diode) display has been made to achieve improved characteristics thereof, and some of the display devices of improved characteristics have already been used in practical applications.
Especially, the home AV equipments are more and more demanded for amusement purposes. The current home AV equipments' market also shows that a consumer's demand is gradually shifted to a larger screen thanks to a reduction in per inch cost. The introduction of the stereophonic sound system also requires home AV equipments to have large screens.
In the business world, there has been an increasing demand for display devices of improved characteristics that offer high visibility effect with easy handling, such as improved brightness not only in still image but also in moving image, that can be suitably used in presentation performance using a computer, etc. To respond to such demand for the described improved characteristics in the business world, a development of display devices of larger screen has been still more expected.
Among such display devices, liquid crystal display devices can be installed even in a small space with ease because of its beneficial features being lighter weight, narrower width, thinner structure than other display devices. Moreover, for other beneficial characteristics of low power consumption and being evolvable into full-color display with ease, the liquid crystal displays' market has been expanded in various fields recently and the development of large-screen liquid crystal display devices has been more strongly demanded than other display devices.
However, when the screen of the liquid crystal display is upsized, as a defect image becomes more noticeable under the same resolution per screen, improvements in the resolution is necessary to achieve quality images of a video source. In the liquid crystal display device, an image is formed by display elements that are integrally formed and can be controlled independently, and thus to increase the number of display elements is inevitable to achieve an improved resolution.
However, the reduction in percent defective of each display element in the manufacturing process already faces the limit, and a significant progress is difficult to be expected.
Namely, to produce a greater number of display elements to meet the demand for the liquid crystal display device of a large screen would accelerate a drop in yield of the display device as a whole. Thus, it would be difficult to mass-produce the liquid crystal display device of a large screen which offers high quality images, and a cost for such liquid crystal display device remains too high.
To overcome the described difficulties, as shown in FIG. 2 of the present embodiment, a method of upsizing a screen using a so-called multi-panel display system has been proposed wherein an image is displayed on a large screen formed by joining plural liquid crystal display panels together. By adopting such system, even with the same percent defective of a single display element, as the defect is dispersed entirely on the display device, an overall improvement of a yield of the liquid crystal display device of a large screen which offers high quality images can be achieved while suppressing an increase in per unit area cost.
When forming a liquid crystal display device of a multi-display system, for example, as shown in FIG. 12(a), liquid crystal panels 52 are joined together. Specifically, the plural liquid crystal panels 52 are joined together so as to be adjacent to one another on a surface of a reinforcing substrate 53 to enable a liquid crystal display device of a still larger screen.
However, when joining plural liquid crystal display panels 52 together to enable such liquid crystal display device of a large screen, if an end surface portion 52c of the liquid crystal panel 52 contacts a medium of different index of refraction (air, etc.), light refraction would occur. Besides, if the end surface portion 52c becomes coarse in the manufacturing process, refraction and scattering of light would occur, thereby presenting the problem that the joint between the liquid crystal panels 52 stands out.
In consideration of the above problems, it is preferable that a hardened bonding agent used in bonding the liquid crystal panels 52 to the reinforcing substrate 53 has the same index of refraction as a hardened bonding agent used in joining the liquid crystal panels 52 together and that the index of refraction of these hardened bonding agents is substantially equal to the index of refraction of the reinforcing substrate 53 and substrates which constitute the liquid crystal panel 52, etc. By arranging so, refraction and scattering of light can be suppressed.
However, as shown in FIG. 12(b), in the case of adopting the bonding agent 59 under the described condition, a crack 59a may generate along the edge of the liquid crystal panels 52. This is because along an edge 52a (see FIG. 12(a)) of the liquid crystal panels 52, as stress concentrates by the curing shrinkage of the bonding agent 59, a crack 59a may be generated or may be expanded even with a small impact. When light passes through such crack 59a, light scattering would occur, which again makes the joint between the liquid crystal panels 52 stand out.
With the described curing shrinkage, a partial pealing 59b occurs between the end surface portion 52c of the connected part of the liquid crystal panels 52 and the bonding agent 59, which would cause the light scattering.
Additionally, when the face precision of the end surface portion 52c is low, since the bonding agent 59 is not spread entirely on the irregularity of the end surface portion 52c, fine bubbles may remain in the space between the end surface portion 52c of the liquid crystal panel 52 and the bonding agent 59. Such fine bubbles remaining in the space may again cause a scattering of light.
Namely, to display a natural image on a large screen, it is required to prevent an occurrence of light scattering, for example, by preventing a generation of the crack 59a, the peeling 59b or bubbles as this makes the joint between the liquid crystal panels 52 noticeable.